For something that affects millions every month, period pain remains surprisingly poorly treated. A recent analysis of supermarket transaction data from more than three million shoppers found that paracetamol is the most purchased painkiller for menstrual cramps—despite being a less effective option than ibuprofen for this particular type of pain. The finding highlights a disconnect between purchasing habits and what the science actually shows works best.

Now, a major review is putting that mismatch into sharp focus. Researchers examined 80 clinical trials involving more than 5,800 women and found that NSAIDs—non-steroidal anti-inflammatory drugs like ibuprofen—were substantially more effective than paracetamol at treating menstrual pain.

The reason comes down to biology. Period pain, or dysmenorrhoea, is caused by hormone-like chemicals called prostaglandins. As the womb lining breaks down each month, the uterus releases these chemicals, triggering strong contractions and reducing blood flow to the uterus, which creates the familiar cramping sensation. Prostaglandins are also linked to inflammation and can cause other effects during a period, such as nausea.

Ibuprofen tackles the root cause. As an NSAID, it blocks cyclooxygenase (Cox) enzymes, which are essential for prostaglandin production. By reducing prostaglandin levels, ibuprofen interrupts the very cascade that leads to menstrual cramps. Paracetamol, by contrast, works mainly in the brain and spinal cord—blocking pain signals from reaching the brain rather than treating the source of that pain. This explains why paracetamol helps with headaches but falls short for period cramps.

Timing matters too. While NSAIDs can reduce period pain when taken at any point, they work best when started one to two days before bleeding begins, continuing through the first couple of days of the period. Taking them ahead of the prostaglandin surge allows them to shut down production before the cramping cascade begins.

For those who find ibuprofen ineffective, other NSAIDs include naproxen and mefenamic acid—the latter sometimes preferred because it may also reduce heavy bleeding, though it requires a prescription. Aspirin is less commonly recommended since it can worsen bleeding due to its blood-thinning properties and isn't advised for those under 16 due to the risk of Reye syndrome.

The good news is that short-term NSAID use is safe for most people. For anyone with asthma, kidney disease, heart problems, a history of stomach ulcers, or those taking blood thinners or certain antidepressants, consulting a healthcare provider first is wise.

With this growing body of evidence, women and anyone who experiences menstrual pain now have clearer guidance: the option sitting in most bathroom cabinets may not be the best one for the job. Knowing the difference—and acting on it—could mean fewer painful days every month.